1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to a manual opening device for manually opening the separable contacts of electrical switching apparatus, such as, for example, circuit breakers. The invention also relates to electrical switching apparatus employing manual opening devices.
2. Background Information
Electrical switching apparatus, such as circuit breakers, provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits and abnormal level voltage conditions. Typically, circuit breakers include a spring powered operating mechanism which opens electrical contacts to interrupt the current through the conductors of an electrical system in response to abnormal conditions.
Under normal operation, relatively large circuit breakers, such as, for example, medium voltage circuit breakers for use in electrical power systems operating at about 1,000 volts or more, are typically supplied with secondary power. This powers a motorized charging mechanism of the operating mechanism and enables the separable contacts of the circuit breaker to be opened or closed relatively easily, for example, by manually pushing the button of a controller disposed on the circuit breaker housing, or remotely, through an electrical connection. However, there must also be a mechanism to manually open the separable contacts in the event of an emergency, damage to the circuit breaker itself, a loss of power or other failure, wherein secondary power might not be available.
Circuit breakers have been known to employ an emergency handle which is accessible at the front face of the circuit breaker housing, and which is structured to be manually actuated in order to trip open the separable contacts. See, for example, U.S. Pat. Nos. 6,373,358 and 6,930,271.
Relatively large (e.g., up to about 3,000 pounds or more) break-away forces are commonly associated with the separation (i.e., opening) of the separable contacts of relatively large (e.g., without limitation, medium voltage) circuit breakers. The break-away force is the force (e.g., magnetic force) which must be exceeded in order to open the separable contacts. It is, therefore, desirable to reduce the amount of physical force that must be exerted in order to operate the manual opening device.
This is particularly true for synchronous switchgear, such as, for example, independent pole operated vacuum circuit breakers wherein manually opening the circuit breaker requires overcoming the cumulative combined break-away forces of a number of separate actuators corresponding to the number of circuit breaker poles. More specifically, in a synchronous circuit breaker, the poles of the circuit breaker and the individual operating mechanisms therefor, are operated independently in order to achieve synchronous switching, commonly referred to in the art as point-on-wave switching. However, each individual operating mechanism has its own associated break-away force. Thus, in the event of a loss of power or other failure, the total combined break-away force of all of the separate operating mechanisms must be overcome to open the separable contacts of the synchronous circuit breaker.
It is desirable, therefore, to provide a manual opening device which is suitable for quickly and easily simultaneously opening the separable contacts of synchronous circuit breakers. It is also desirable to provide such a manual opening device which accomplishes the foregoing through use of a single opening device as opposed to requiring separate opening devices for each pole and associated operating mechanism therefor, of the synchronous circuit breaker. It is further desirable that the manual opening device be relatively easy to employ through use of a minimal amount of physical effort.
There is, therefore, room for improvement in electrical switching apparatus, such as for example, synchronous circuit breakers, and in manual opening devices therefor.